The present invention relates to systems for aiding physically impaired persons in ascending or descending stairways. More particularly, the invention is directed to a motorized portable system which can be used transferably with a virtually unlimited number of different stairways to minimize cost, and which nevertheless is extremely safe and reliable.
The majority of previously developed systems are permanent installations. In such systems a motorized moving handgrip or a motorized supporting platform or chair is permanently mounted in conjunction with a particular stairway so that a person can walk or ride up or down the stairway with the aid of the device. A principal drawback of a permanent installation is that a separate motorized system is needed for each separate stairway, thereby maximizing the capital cost for each stairway and thus severely limiting the number and locations of stairways for which the system is usable. Systems of this general type are exemplified by the following publications:
U.S. Pat. No. 4,602,567 PA0 U.S. Pat. No. 4,904,916 PA0 U.S. Pat. No. 4,913,264 PA0 U.S. Pat. No. 5,050,708 PA0 U.S. Pat. No. 5,052,521 PA0 German Patent Publication No. DE 3934431A1 PA0 German Utility Model G8710943.3 PA0 German Utility Model G8217206.4 PA0 French Patent Publication No. 2517287 PA0 Japanese Utility Model Publication No. 60-43678 PA0 Japanese Utility Model Publication No. 1-58584 PA0 Japanese Patent Publication No. 3-61278 PA0 LIFTA Treppenlifte brochure (undated) published by LIFTA GmbH of Cologne, Germany. PA0 HIRO LIFT brochure (undated) published by Hillenkotter & Ronsieck GmbH of Bielefeld, Germany.
Another general class of prior systems consists of free-standing stair-climbing vehicles. These units require no mounting whatsoever of hardware on each stairway, and thus possess the adaptability for use with different stairways which the permanent installations lack. However, these systems, as exemplified by U.S. Pat. Nos. 3,573,877 and 3,592,282, must depend on proper stair surface conditions and friction for adequate traction, and upon proper weight distribution for stability, neither of which is reliable from a safety standpoint. Alternatively, such systems could include their own portable tracks, as shown in U.S. Pat. No. 4,564,086, but this would severely restrict their versatility for use with different lengths and slopes of stairways.
A few systems have been conceived in the past in which an assisting device can detachably engage a stair-mounted track to provide a reliable tractive and stable interconnection with the stairway, and yet can be used transferably on other similarly tracked stairways. U.S. Pat. No. 4,253,287 shows a nonmotorized handgrip which detachably engages tracks on both sides of a stairway and thus may be portably transferred between the tracks of different stairways. However, motorizing such a handgrip in a manner consistent with its detachability from the track is highly problematic. Japanese Utility Model Publication No. 58-20271 shows a wheelchair detachably connectable to a stairway track assembly. Although the wheelchair would apparently be transferable between the respective tracks of different stairways, the wheel-chair has no mechanism for adjusting to tracks and stairways of different slopes without affecting the horizontal attitude of the wheelchair, and engagement of tracks located on different sides of respective stairways is possible only by disassembling and remounting a trackengaging pinion. Moreover, the extremely forward position of the pinion relative to the wheelchair requires that the track extend significantly beyond the top or bottom of the stairway to enable the wheelchair to be stably positioned before it is disengaged from the track. Such a track extension is impossible in the common situation where a hallway transversely intersects the top or bottom of a stairway. In addition, the track engagement pinion of the wheelchair projects permanently outwardly of the wheels thereby inhibiting the ability of the wheelchair to pass through narrow spaces.